Humic acid is a principal component of humic substances, which is the major organic constituents of soil, coal, peat, many upland streams, dystrophic lakes, and ocean water. It is produced by the biodegradation of dead organic matters. Humic substances contain major groups for chemistry, such as polyphenols, polycarboxylic acids, carbonyl groups, and peroxides. The presence of carboxylate and phenolate groups gives the humic acids the ability to form complexes with ions such as, Fe2+, Fe3+, Mg2+, and Ca2+.Acetylcholinesterase (AChE, E.C.3.1.1.7), also known as AChE, is a hydrolase that hydrolyses the neurotransmitter acetylcholine. AChE is found at mainly neuromuscular junctions and cholinergic brain synapses, where its activity serves to terminate synaptic transmission. Reduction in the activity of the cholinergic neurons is a well-known property of Alzheimer's disease. Acetylcholinesterase inhibitors are employed to reduce the rate at which acetylcholine (ACh) is broken down, so that increasing the concentration of ACh in the brain and fighting the loss of ACh caused by the death of cholinergic neurons. Natural compounds are very important for Alzheimer's disease. Humic substances are the major natural bio-polyelectrolyte and contain major groups for chemistry.In this study, the effect of humic acid was investigated on acetylcholinesterase (AChE) and bu-tyrylcholinesterase (BChE, E.C.3.1.1.8) enzymes. AChE and BChE inhibition studies were performed according to Ellman method. IC50 and Ki values were calculated for humic acid. These values were found 0.474 and 0.181 nM for AChE and 20.83 and 0.208 nM for BChE, respectively. The inhibition type was determined as competitive.
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